Two business associates visiting New York casually strolled into the iconic “21” club for a weeknight supper this summer — and left 90 minutes later after plunking down $16,640 on a pair of Petrus ’82 wine bottles, the world’s rarest and most expensive Bordeaux vintage.

“It’s one of the most famous wines in the world,” said Phil Pratt, wine director and à la carte sommelier at “21,” who said the famed restaurant has records of selling only five other bottles over the past three decades.

The last time Pratt sold a Petrus ’82 was years ago at a posh private birthday celebration in the wine cellar.

“It’s not a wine we normally sell,” said Pratt, whose jaw almost dropped when a pair of diners appeared to order two bottles on a whim.

The two businessmen, who had never dined at “21” before, arrived at 8:30 p.m. and ordered light appetizers, followed by the $65 dover sole and the $39 steelhead salmon. One of the men selected the $8,320 bottle from the wine list for him and his guest.

“The gentleman knew what he was ordering,” Pratt said. “It was a little strange, especially when one of the guys was drinking coffee throughout the meal, too. But I don’t judge. It’s their money; they can do what they want with it. If he wants Coca-Cola in his wine, I’m OK with that.”

The thirsty duo had drained their first bottle while finishing their appetizers — a Caesar salad and the peekytoe crab salad — and summoned the sommelier over to lubricate them through entrees and into dessert.

“He said ‘bring us another one,’ ” recalled Pratt. “At that point, you smile, and you try not to jump up and down and wave your arms too much.”

The rare Petrus ’82 was produced from merlot grapes on a small estate in Saint-Emilion, France. At “21,” the sommelier has records of ordering 12 of the showy bottles when it came on the market.

After three decades, he’s now down to three bottles and may raise the price on the rare commodity. Pratt said he’s not likely to try and restock when he runs dry.

“There’s been a lot of counterfeiting of this wine,” he said. “There’s an old saying that more bottles of ’82 Petrus have been sold in Las Vegas than ever existed. We would never buy a bottle unless we knew it was straight from the cellar.”

The total bill for the evening came out to $18,737.18 — including $1,494.68 in tax and a $400 tip. For the big spenders, the restaurant threw in two cookies.